fabricating engine mount supports

redlinj

Petty Officer 1st Class
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Oct 4, 2007
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250
After blowing my engine(3.7/485) and outdrive the decision has been made to repower with a 5.7 260hp. And appropriate 1.5 outdrive. As my Grady White's stringers are 26.5" apart on center I will have to do some fabricating as the 350 engine mounts are 22.5" apart. Was thinking the simplest way to do this would be to take some 3" angle and thru bolt it to the inside of each stringer, but playing devil's advocate, was thinking that the 250lbs of additional weight might add too much torque to the stringers. I'd like to think that I am over thinking this too much! I'm sure others out there have repowered their 3.7's with V8's or 6s. Any alternative methods? Thanks
 

gm280

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Jun 26, 2011
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redlinj, while I have never done what you're talking about, physics rules the effort every time. I think you're on the right track but would install something under the angle material ( and I would use either Stainless steel or aluminum) to help support the additional weight. That way both the side of the stringers AND the hull itself will support the engine. So design a setup with angle aluminum and then polyester additional material under the angle and I think it will work. There would be so much less torque imposed on the stringers that way. So no change of tearing the stringers out... JMHO!
 

81 Checkmate

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Jul 20, 2010
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gm280 is on the right track. I would be woried that the angles on the sides of stringers would put alot of strees inward on each stringer. Seeing how your stringers are farther apart than needed - Add more wood inward and encase in fiberglass - Then bolt a flat plate across the two to strenghten them up. Then go with the normal V-8 mounts. Drill your 2 holes and lag into the new wood suports. Head over to the resto section and ask the question. those guys are wizards when it comes to this stuff.

Good Luck!
 

Bondo

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Apr 17, 2002
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70,464
Ayuh,.... I'd rather build wood, 'n glass mountin' blocks, than hang it off steel mounts myself,....
 
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redlinj

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Oct 4, 2007
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250
Yes, I have to agree that the main support should come from directly under to eliminate as much stress on the main stringers as possible. I see the light! What might be a good material to use to shoulder this load? I believe I can fab something up now to get this boat back on the water! Thanks guys!!!
 

Bondo

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Ayuh,.... Plywood, glass,'n resin,..??
 

redlinj

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Oct 4, 2007
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250
Just out of curiosity, is there any synthetic material that might be used in place of wood??
 

redlinj

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Oct 4, 2007
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250
OK, how ?bout if this is approached from a different angle. What would happen if a 2" spacer was placed between the engine and bracket that the mount is bolted to? This would widen the mounts and set them down dead center on the present stringers. Haven't taken any measurements yet as I just thought of it but it seems like it could work-----in theory anyway. OK all you devil advocates out there, what say you!
 

redlinj

Petty Officer 1st Class
Joined
Oct 4, 2007
Messages
250
OK, how ?bout if this is approached from a different angle. What would happen if a 2" spacer was placed between the engine and bracket that the mount is bolted to? This would widen the mounts and set them down dead center on the present stringers. Haven't taken any measurements yet as I just thought of it but it seems like it could work-----in theory anyway. OK all you devil advocates out there, what say you!

After searching and searching, I accidently came up with a somewhat modified motor mount setup from a company called marineenginedepot.com. They have beefed up mount brackets and longer trunion pins that will adjust out that extra inch or so on each side so as to place the engine weight directly over the stingers. For the price, it was well worth not having to deal with trying to fab in new support stringers. Now the boat has not been tested in the water yet but when it is, i'll let you all know how the 5.7 moves the boat compared to the 3.7! http://forums.iboats.com/forum/boat...03694-fabricating-engine-mount-supportsingers
 
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